Treatment of wells



Patented May 19, 1942 UNl'lED STATES PATET, o-FFIc-E 2,283,563 TREATMENT or WELLS Q No Drawing. Application Januaryl9, 1940,

Serial N0. 314,693

Claims. (01. 166- 21.)

The invention relates to a method of removing a. selected section or portion of the iron or steel casingused to line the bore hole of wells such as,

for example, oil wells. Wells drilled for the production of oil, gas or other mineral fluids are usually lined with iron or steel pipe over a considerable portion of-their depth. This steel pipe, generally known as thewell casing; is usually cemented in place at a point above the productive stratum'in-which the well is first completed and acts to prevent the walls of the well bore from caving, as well as preventing the infiltration of undesirable fluids into the well bore.

In some instances it may be desirable at a later date to remove certain portions or sections of the well casing in order to expose other formations to production. For example, wells oftentimes pass through several strata of a productive nature before the well is completed in the stratum from which it is desired to obtain production. As the well continues to be produced, the flow of the desired mineral fluid falls off' to the extent that it isdesirable to open up other sections to production. g

It has been proposed to remove any desired section of the steel casing by a drilling or milling operation. However, the proposed method is not entirely satisfactory due to the fact that it is extremely diiiicult to operate a drill deep in the well so as to cut out a section of the casing, especially if the operation is to be carried out so as to entirely remove a section over an extended length. 7

'It is, therefore, the principal object of the invention to provide a method whereby any desired ammunt of a well casing comprised essentially of ferrous metal can be readily and completely removed.

Other 'objects and advantages will be apparent highly advantageous and essential, because it furnishes a means whereby the action of a highly corrosive chemical solution can be confined or localized, thus making it possible to reniove only a desired or selected section of the casing. Without the use of pressure, I have found that the heat generated by the reaction between the highly-corrosive chemical solutions and the steel causes the solution to boil so violentlythat it rises to great heights in the well bore and thus 5 dissipates: itself over an area of unpredictable extent. 1

Incarrying out the method of the invention in an oil well, for example,'wherein it is desired to remove ,only a selected section of the steel l o casing, the following procedure is employed.

I The well is first sealed off 'at the lower-level of the section to be removed, as by running a conventional packer into the well and seating it at the desired location. An amount of corrosive chemical solution calculated to. fill the well casing over the section to be removed is then lowered into the well in a conventional well bailer and deposited on top of the packer or other sealing means. The well is then closed in and pressure is applied at the well casing head, as by time has elapsed to bring the section of steel casing contacted by the corrosive chemical into solution.

It is usually desirable to allow the chemical solution to remain in contact with the casing for from 2 to 4 hours or more, and in many instances the chemical solution should be replaced one or I more times in order to bring about satisfactory removal of the steel casing. The amount of solution required can be readily calculated from a knowledge of the amountof steel or iron to be removed and the concentration of solution employed. The amount of pressure to be employed varies quite widely depending upon the heat generated by the reaction.l In general, pressures of 40 from between about 100 pounds per square inch up to the critical pressure of the solution employed have been found to be satisfactory. Pressures in this order do not noticeably retard th e rate of reaction of the corrosive chemicals upon iron or steel.

Among the corrosive chemical solutions that I have found desirable for the purpose at hand are those characterized by having a strong oxidizing action on iron or steel and giving an acid reaction. In addition, they boil at atmospheric pressure when chemically acting upon and dissolving iron or steel. For example, mixtures of hydrochloric and nitric acids containing from 2 to 4 parts by volume of concentrated hydrochloric acid to 1 part by volume of concentrated nitric ture.

acid are suitable, This hydrochloric acid-nitric acid mixture may be suitably employed in a diluted state wherein at least 80 per cent of the solution is comprised of concentrated acid mix- Another suitable corrosive chemical solution consists of a mixture of sulfuric and nitric acids in the ratio of from 1 to 3 parts of concentrated sulfuric to 1 part by volume of concentrated nitric acid. This solution should be employed in a diluted state such that the mixture of concentrated acids comprises from 30 to 60 per cent by volume of the diluted solution.

Other solutions of this general nature may be suitably employed. The corrosive solution may be agitated, if desired, to increase the rate of reaction while it is held at the desired location in the well bore under pressure.

Thus, by suitably controlling the corrosive soiution under pressure, any selected section of an iron or steel casing can be readily and rapidly removed.- In some instances, cement may extend up around the section of steel casing. In such cases, the cement can be readily removed, as by setting off a small charge of explosive adjacent the cement, which causes it to slough away from the bore walls and allows the flow of the desired mineral fluid into the well.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be em- ,ployed.

I therefore particularly point out and distinctly claim as my invention:

1. In a method of removing a section of well casing comprised essentially of a ferrous metal with a highly corrosive chemical solution which boils when chemically dissolving a ferrous metal, the steps which consist in filling the casing with the corrosive chemical solution adjacent the section to be removed, and thereafter applying pressure uponthe corrosive chemical'solution in an amount sufiicient to prevent the solution from boiling.

2. In a method of removing a section of well casing comprised essentially of iron with a chemical solution of the type having an oxidizing action on iron and an acid reaction, said solution being further characterized by boiling when chemically dissolving iron, the steps which consist in filling the casing with the chemical solution adjacent the section to be removed, and thereafter applying pressure upon the chemical solution in an amount from between about 100 pounds per square inch up to the critical-pressure of the solution.

3. In a method of removing a section of well casing comprised essentially of iron with a chemical solution of the type having an oxidizing action on iron and an acid reaction, said solution being further characterized by boiling when chemically dissolving iron, the steps which consist in sealing olf the portion of the well bore below the section to be removed, filling the casing with the chemical solution adjacent the section to be removed, and thereafter applying pressure 4 upon the chemical solution in an amount from between about 100 pounds per square inch up to the critical pressureof the chemical solution.

4. In a method of removing a section of a well casing -comprised essentially of iron, the steps which consist in introducing into the well an aqueous solution containing between about 80 to 100 per cent by volume of a mixture comprising 1 part by volume of concentrated nitric acid and from 2 to 4 parts by volume of concentrated hydrochloric acid in an amount sufiicient to fill the well casing over the section to be removed, and

thereafter applying pressure upon the mixture of acids in an amount suflicient to prevent them from boiling.

5. In a method of removing a section of a well casing comprised essentially of iron, the steps which consist in introducing into the well an aqueous solution containing between 30 to per cent by volume of a mixture comprising 1 part by volume of concentrated nitric acid and from 1 to 3 parts by volume of concentrated sulfuric acid in an amount sufilcient to fill the casing over the section to be removed, and thereafter applying pressure upon the mixture in an amount sufficient to keep the mixture from boil- ORLIN W. LYONS. 

